enhance jump threading to preserve TBAA information when PRE'ing loads,

fixing rdar://11039258, an issue that came up when inspecting clang's 
bootstrapped codegen.

llvm-svn: 152635

include/llvm/Analysis/Loads.h

@@ -20,6 +20,7 @@ namespace llvm {
 
 class AliasAnalysis;
 class TargetData;
+class MDNode;
 
 /// isSafeToLoadUnconditionally - Return true if we know that executing a load
 /// from this value cannot trap.  If it is not obviously safe to load from the
@@ -41,10 +42,15 @@ bool isSafeToLoadUnconditionally(Value *V, Instruction *ScanFrom,
 /// MaxInstsToScan specifies the maximum instructions to scan in the block.
 /// If it is set to 0, it will scan the whole block. You can also optionally
 /// specify an alias analysis implementation, which makes this more precise.
+///
+/// If TBAATag is non-null and a load or store is found, the TBAA tag from the
+/// load or store is recorded there.  If there is no TBAA tag or if no access
+/// is found, it is left unmodified.
 Value *FindAvailableLoadedValue(Value *Ptr, BasicBlock *ScanBB,
                                 BasicBlock::iterator &ScanFrom,
                                 unsigned MaxInstsToScan = 6,
-                                AliasAnalysis *AA = 0);
+                                AliasAnalysis *AA = 0,
+                                MDNode **TBAATag = 0);
 
 }
 

lib/Analysis/Loads.cpp

@@ -17,6 +17,7 @@
 #include "llvm/GlobalAlias.h"
 #include "llvm/GlobalVariable.h"
 #include "llvm/IntrinsicInst.h"
+#include "llvm/LLVMContext.h"
 #include "llvm/Operator.h"
 using namespace llvm;
 
@@ -160,10 +161,15 @@ bool llvm::isSafeToLoadUnconditionally(Value *V, Instruction *ScanFrom,
 /// MaxInstsToScan specifies the maximum instructions to scan in the block.  If
 /// it is set to 0, it will scan the whole block. You can also optionally
 /// specify an alias analysis implementation, which makes this more precise.
+///
+/// If TBAATag is non-null and a load or store is found, the TBAA tag from the
+/// load or store is recorded there.  If there is no TBAA tag or if no access
+/// is found, it is left unmodified.
 Value *llvm::FindAvailableLoadedValue(Value *Ptr, BasicBlock *ScanBB,
                                       BasicBlock::iterator &ScanFrom,
                                       unsigned MaxInstsToScan,
-                                      AliasAnalysis *AA) {
+                                      AliasAnalysis *AA,
+                                      MDNode **TBAATag) {
   if (MaxInstsToScan == 0) MaxInstsToScan = ~0U;
 
   // If we're using alias analysis to disambiguate get the size of *Ptr.
@@ -191,15 +197,19 @@ Value *llvm::FindAvailableLoadedValue(Value *Ptr, BasicBlock *ScanBB,
     // (This is true even if the load is volatile or atomic, although
     // those cases are unlikely.)
     if (LoadInst *LI = dyn_cast<LoadInst>(Inst))
-      if (AreEquivalentAddressValues(LI->getOperand(0), Ptr))
+      if (AreEquivalentAddressValues(LI->getOperand(0), Ptr)) {
+        if (TBAATag) *TBAATag = LI->getMetadata(LLVMContext::MD_tbaa);
         return LI;
+      }
     
     if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
       // If this is a store through Ptr, the value is available!
       // (This is true even if the store is volatile or atomic, although
       // those cases are unlikely.)
-      if (AreEquivalentAddressValues(SI->getOperand(1), Ptr))
+      if (AreEquivalentAddressValues(SI->getOperand(1), Ptr)) {
+        if (TBAATag) *TBAATag = SI->getMetadata(LLVMContext::MD_tbaa);
         return SI->getOperand(0);
+      }
       
       // If Ptr is an alloca and this is a store to a different alloca, ignore
       // the store.  This is a trivial form of alias analysis that is important

lib/Transforms/Scalar/JumpThreading.cpp

@@ -857,6 +857,9 @@ bool JumpThreading::SimplifyPartiallyRedundantLoad(LoadInst *LI) {
   if (BBIt != LoadBB->begin())
     return false;
 
+  // If all of the loads and stores that feed the value have the same TBAA tag,
+  // then we can propagate it onto any newly inserted loads.
+  MDNode *TBAATag = LI->getMetadata(LLVMContext::MD_tbaa); 
 
   SmallPtrSet<BasicBlock*, 8> PredsScanned;
   typedef SmallVector<std::pair<BasicBlock*, Value*>, 8> AvailablePredsTy;
@@ -875,11 +878,16 @@ bool JumpThreading::SimplifyPartiallyRedundantLoad(LoadInst *LI) {
 
     // Scan the predecessor to see if the value is available in the pred.
     BBIt = PredBB->end();
-    Value *PredAvailable = FindAvailableLoadedValue(LoadedPtr, PredBB, BBIt, 6);
+    MDNode *ThisTBAATag = 0;
+    Value *PredAvailable = FindAvailableLoadedValue(LoadedPtr, PredBB, BBIt, 6,
+                                                    0, &ThisTBAATag);
     if (!PredAvailable) {
       OneUnavailablePred = PredBB;
       continue;
     }
+    
+    // If tbaa tags disagree or are not present, forget about them.
+    if (TBAATag != ThisTBAATag) TBAATag = 0;
 
     // If so, this load is partially redundant.  Remember this info so that we
     // can create a PHI node.
@@ -939,6 +947,9 @@ bool JumpThreading::SimplifyPartiallyRedundantLoad(LoadInst *LI) {
                                  LI->getAlignment(),
                                  UnavailablePred->getTerminator());
     NewVal->setDebugLoc(LI->getDebugLoc());
+    if (TBAATag)
+      NewVal->setMetadata(LLVMContext::MD_tbaa, TBAATag);
+    
     AvailablePreds.push_back(std::make_pair(UnavailablePred, NewVal));
   }
 

test/Transforms/JumpThreading/thread-loads.ll

@@ -1,12 +1,12 @@
 ; RUN: opt < %s -jump-threading -S | FileCheck %s
-; rdar://6402033
 
-; Test that we can thread through the block with the partially redundant load (%2).
 target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128"
 target triple = "i386-apple-darwin7"
 
-define i32 @foo(i32* %P) nounwind {
-; CHECK: foo
+; Test that we can thread through the block with the partially redundant load (%2).
+; rdar://6402033
+define i32 @test1(i32* %P) nounwind {
+; CHECK: @test1
 entry:
 	%0 = tail call i32 (...)* @f1() nounwind		; <i32> [#uses=1]
 	%1 = icmp eq i32 %0, 0		; <i1> [#uses=1]
@@ -39,3 +39,43 @@ bb3:		; preds = %bb1
 declare i32 @f1(...)
 
 declare i32 @f2(...)
+
+
+;; Check that we preserve TBAA information.
+; rdar://11039258
+
+define i32 @test2(i32* %P) nounwind {
+; CHECK: @test2
+entry:
+	%0 = tail call i32 (...)* @f1() nounwind		; <i32> [#uses=1]
+	%1 = icmp eq i32 %0, 0		; <i1> [#uses=1]
+	br i1 %1, label %bb1, label %bb
+
+bb:		; preds = %entry
+; CHECK: bb1.thread:
+; CHECK: store{{.*}}, !tbaa !0
+; CHECK: br label %bb3
+	store i32 42, i32* %P, align 4, !tbaa !0
+	br label %bb1
+
+bb1:		; preds = %entry, %bb
+	%res.0 = phi i32 [ 1, %bb ], [ 0, %entry ]
+	%2 = load i32* %P, align 4, !tbaa !0
+	%3 = icmp sgt i32 %2, 36
+	br i1 %3, label %bb3, label %bb2
+
+bb2:		; preds = %bb1
+	%4 = tail call i32 (...)* @f2() nounwind
+	ret i32 %res.0
+
+bb3:		; preds = %bb1
+; CHECK: bb3:
+; CHECK: %res.01 = phi i32 [ 1, %bb1.thread ], [ 0, %bb1 ]
+; CHECK: ret i32 %res.01
+	ret i32 %res.0
+}
+
+!0 = metadata !{metadata !"int", metadata !1}
+!1 = metadata !{metadata !"omnipotent char", metadata !2}
+!2 = metadata !{metadata !"Simple C/C++ TBAA", null}
+